We have studied the kinematic properties of young pre-main-sequence stars. We have selected these stars based on data from the Gaia DR2 catalogue by invoking a number of photometric infrared surveys. Using 4564 stars with parallax errors less than 20\%, we have found the following parameters of the angular velocity of Galactic rotation: $Ω_0 =28.84\pm0.10$ km s$^{-1}$ kpc$^{-1}$, $Ω^{'}_0=-4.063\pm0.029$ km s$^{-1}$ kpc$^{-2}$ and $Ω^{''}_0=0.766\pm0.020$ km s$^{-1}$ kpc$^{-3}$, where the Oort constants are $A=16.25\pm0.33$ km s$^{-1}$ kpc$^{-1}$ and $B=-12.58\pm0.34$ km s$^{-1}$ kpc$^{-1}$. The circular rotation velocity of the solar neighborhood around the Galactic center is $V_0=230.7\pm4.4$ km s$^{-1}$ for the adopted Galactocentric distance of the Sun $R_0=8.0\pm0.15$ kpc. The residual velocity dispersion for the stars considered is shown to be low, suggesting that they are extremely young. The residual velocity dispersion averaged over three coordinates is $\sim$11 km s$^{-1}$ for Herbig Ae/Be stars and $\sim$7 km s$^{-1}$ for T Tauri stars.
We investigate of the systems of proper motions of stars in the ground-based catalogues HSOY, UCAC5, GPS1 and PMA derived by combining with the Gaia DR1 space data. Assuming the systematic differences of stellar proper motions of two catalogues to be caused by the mutual solid-body rotation and glide of the coordinate systems produced by the data of the catalogues under comparison, we analyse the components of the mutual rotation vector and displacement of the origins of these systems. The equatorial components of the vector of mutual rotation velocity of the compared coordinate systems, as we…
Recently, the first installment of data from ESA's Gaia astrometric satellite mission (Gaia-DR1) was released, containing positions of more than 1 billion stars with unprecedented precision, as well as only proper motions and parallaxes, however only for a subset of 2 million objects. The second release, due in late 2017 or early 2018, will include those quantities for most objects. In order to provide a dataset that bridges the time gap between the Gaia-DR1 and Gaia-DR2 releases and partly remedies the lack of proper motions in the former, HSOY ("Hot Stuff for One Year") was created as a hybr…
We present a panoramic map of the stellar streams of the Milky Way based upon astrometric and photometric measurements from the Gaia DR2 catalogue. In this first contribution, we concentrate on the halo at heliocentric distances beyond 5 kpc, and at Galactic latitudes $|b|>30°$, using the STREAMFINDER algorithm to detect structures along plausible orbits that are consistent with the Gaia proper motion measurements. We find a rich network of criss-crossing streams in the halo. Some of these structures were previously-known, several are new discoveries, but others are potentially artefacts of th…
In this first paper we simulate the population of disc Red Clump stars to be observed by Gaia. We generate a set of test particles and we evolve it in a 3D barred Milky Way like galactic potential. We assign physical properties of the Red Clump trace population and a realistic 3D interstellar extinction model. We add Gaia observational constraints and an error model according to the pre-commissioning scientific performance assessments. We present and analyse two mock catalogues, offered to the community, that are an excellent test bed for testing tools being developed for the future scientific…
We present two catalogues of active galactic nucleus (AGN) candidates selected from the latest data of two all-sky surveys -- Data Release 2 (DR2) of the \emph{Gaia} mission and the unWISE catalogue of the \emph{Wide-field Infrared Survey Explorer} (\emph{WISE}). We train a random forest classifier to predict the probability of each source in the \emph{Gaia}-unWISE joint sample being an AGN, $P_{\rm RF}$, based on \emph{Gaia} astrometric and photometric measurements and unWISE photometry. The two catalogues, which we designate C75 and R85, are constructed by applying different $P_{\rm RF}$ thr…
Aims: An effort has been undertaken to simulate the expected Gaia Catalogue, including the effect of observational errors. A statistical analysis of this simulated Gaia data is performed in order to better understand what can be obtained from the Gaia astrometric mission. This catalogue is used in order to investigate the potential yield in astrometric, photometric and spectroscopic information, and the extent and effect of observational errors on the true Gaia Catalogue. This article is a follow-up to Robin et. al. (2012), where the expected Gaia Catalogue content was reviewed but without the…
We have searched for the stars that either encountered in the past or will encounter in the future with the Solar system closer than 2 pc. For this purpose, we took more than 216 000 stars with the measured proper motions and trigonometric parallaxes from the Gaia DR1 catalogue and their radial velocities from the RAVE5 catalogue. We have found several stars for which encounters closer than 1 pc are possible. The star GJ 710, for which the minimum distance is d_m=0.063+/-0.044 pc at time t_m=1385+/-52 thousand years, is the record-holder among them. Two more stars, TYC 8088-631-1 and TYC 6528-…
The third Gaia data release is published in two stages. The early part, Gaia EDR3, gives very precise astrometric and photometric properties for nearly two billion sources together with seven million radial velocities from Gaia DR2. The full release, Gaia DR3, will add radial velocities, spectra, light curves, and astrophysical parameters for a large subset of the sources, as well as orbits for solar system objects. Before the publication of the catalogue, many different data items have undergone dedicated validation processes. The goal of this paper is to describe the validation results in te…
We have studied a sample of more than 25 000 young stars with proper motions and trigonometric parallaxes from the Gaia DR2 catalogue. The relative errors of their parallaxes do not exceed 10\%. The selection of stars belonging to active star-forming regions was made by Marton et al. based on data from the Gaia DR2 catalogue by invoking infrared measurements from the WISE and Planck catalogues. Low-mass T Tauri stars constitute the majority of sample stars. The following parameters of the angular velocity of Galactic rotation have been found from them: $Ω_0 =28.40\pm0.11$ km s$^{-1}$ kpc$^{-1}…
In light of substantial new discoveries of hot subdwarfs by ongoing spectroscopic surveys and the availability of the Gaia mission Early Data Release 3 (EDR3), we compiled new releases of two catalogues of hot subluminous stars: The data release 3 (DR3) catalogue of the known hot subdwarf stars contains 6,616 unique sources and provides multi-band photometry, and astrometry from Gaia EDR3 as well as classifications based on spectroscopy and colours. This is an increase of 742 objects over the DR2 catalogue. This new catalogue provides atmospheric parameters for 3,087 stars and radial velocitie…
The occurrence of multiple stars, dominantly binaries, is studied using the \textit{Gaia}-ESA DR2 catalogue. We apply the optimized statistical method that we previously developed for the analysis of 2D patterns. The field of stars is divided into a mosaic of small pieces, which represent a statistical set for analysis. Specifically, data input is represented by a grid of circles (events) with radius $0.02\,°$ covering the sky in the field of galactic latitude $\left\vert b\right\vert >25\,°$. The criteria for selecting candidates for multiple stars are based on two parameters: angular separat…
Gaia DR3 and further releases have the potential to identify and categorise new emission-line stars in the Galaxy. We perform a comprehensive validation of astrophysical parameters from Gaia DR3 with the spectroscopically estimated emission-line star parameters from LAMOST OBA emission catalogue. We compare different astrophysical parameters provided by Gaia DR3 with those estimated using LAMOST spectra. By using a larger sample of emission-line stars, we perform a global polynomial and piece-wise linear fit to update the empirical relation to convert Gaia DR3 pseudo-equivalent width to observ…
We study the kinematics of a sample of classical Cepheids younger than 120 Myr. For these stars, the estimates of distances taken from Skowron et al., which are based on the period-luminosity relation, and the line-of-sight velocities and the proper motions from the Gaia catalog are available. There are also distance estimates derived from the trigonometric parallaxes contained in the Gaia ERD3 catalog. A method, which relies on comparison of the first-order derivative of the Galactic rotation angular velocity, showed the need to lengthen the distance scales determined by Skowron et al. by abo…
In preparation for the upcoming all-sky data releases of the Gaia mission we compiled a catalogue of known hot subdwarf stars and candidates drawn from the literature and yet unpublished databases. The catalogue contains 5613 unique sources and provides multi-band photometry from the ultraviolet to the far infrared, ground based proper motions, classifications based on spectroscopy and colours, published atmospheric parameters, radial velocities and light curve variability information. Using several different techniques we removed outliers and misclassified objects. By matching this catalogue …
Based on data from the ESA Gaia Data Release 2 (DR2) and several ground-based, multi-band photometry surveys we compiled an all-sky catalogue of $39\,800$ hot subluminous star candidates selected in Gaia DR2 by means of colour, absolute magnitude and reduced proper motion cuts. We expect the majority of the candidates to be hot subdwarf stars of spectral type B and O, followed by blue horizontal branch stars of late B-type (HBB), hot post-AGB stars, and central stars of planetary nebulae. The contamination by cooler stars should be about $10\%$. The catalogue is magnitude limited to Gaia $G<19…
In light of substantial new discoveries of hot subdwarfs by ongoing spectroscopic surveys and the availability of new all-sky data from ground-based photometric surveys and the Gaia mission Data Release 2, we compiled an updated catalogue of the known hot subdwarf stars. The catalogue contains 5874 unique sources including 528 previously unknown hot subdwarfs and provides multi-band photometry, astrometry from Gaia, and classifications based on spectroscopy and colours. This new catalogue provides atmospheric parameters of 2187 stars and radial velocities of 2790 stars from the literature. Usi…
We have analyzed the space velocities of stars with the proper motions and trigonometric parallaxes from the Gaia TGAS catalogue in combination with the line-of-sight velocities from the RAVE5 catalogue. In the (V,\sqrt{U^2+2V^2}) velocity plane we have identified three clumps, BB17-1, BB17-2, and BB17-3, in the region of large velocities (V<-150 km/s). The stars of the BB17-1 and BB17-2 clumps are associated with the kinematic groups VelHel-6 and VelHel-7 detected previously by Helmi et al. We give the greatest attention to the BB17-3 clump. The latter is shown to be most closely linked with …
We present and analyse mock stellar catalogues that match the selection criteria and observables (including uncertainties) of the Gaia satellite data release 2 (DR2). The source are six cosmological high-resolution magneto-hydrodynamic $Λ$CDM zoom simulations of the formation of Milky Way analogues from the AURIGA project. Mock data are provided for stars with $V < 16$ mag, and $V < 20$ mag at $|b|>20$ degrees. The mock catalogues are made using two different methods: the public SNAPDRAGONS code, and a method based on that of Lowing et al. that preserves the phase-space distribution of the mod…
Context: Blue horizontal-branch stars are very old objects that can be used as markers in studies of the Galactic structure and formation history. To create a clean sky catalogue of blue horizontal-branch stars, we cross-matched the Gaia data release 2 (DR2) dataset with existing reference catalogues to define selection criteria based on Gaia DR2 parameters. Following the publication of Gaia early data release 3 (EDR3), these methods were verified and subsequently applied to this latest release. Aims: The purpose of this catalogue is to identify a set of blue horizontal-branch star candidates …
We have analyzed the kinematics of OB stars from the list by Xiang et al. (2021) that contains $\sim$13 000 single OB stars. For these stars there are photometric distance estimates and proper motions from the Gaia catalogue and line-of-sight velocities from the LAMOST catalogue. Based on a sample of single OB stars and using the photometric distances and proper motions of stars from the Gaia EDR3 catalogue, we have found the group velocity components $(U_\odot,V_\odot,W_\odot)=(9.63,9.93,7.45)\pm(0.27,0.34,0.10)$ km s$^{-1}$, and the following parameters of the angular velocity of Galactic ro…
State-of-the-art techniques to identify Hαemission line sources in narrow-band photometric surveys consist of searching for Hαexcess with reference to nearby objects in the sky (position-based selection). However, while this approach usually yields very few spurious detections, it may fail to select intrinsically faint and/or rare Hα-excess sources. In order to obtain a more complete representation of the heterogeneous emission line populations, we recently developed a technique to find outliers relative to nearby objects in the colour-magnitude diagram (CMD-based selection). By combining posi…
We have studied the simultaneous and separate solutions of the basic kinematic equations obtained using the stellar velocities calculated on the basis of data from the Gaia TGAS and RAVE5 catalogues. By comparing the values of Omega_0' found by separately analyzing only the line-of-sight velocities of stars and only their proper motions, we have determined the distance scale correction factor p to be close to unity, 0.97+/-0.04. Based on the proper motions of stars from the Gaia TGAS catalogue with relative trigonometric parallax errors less than 10% (they are at a mean distance of 226 pc), we…
Context. Planetary nebulae (PNe) are a brief but important phase of stellar evolution. The study of Galactic PNe has historically been hampered by uncertain distances, but the parallaxes of PN central stars (CSPNe) measured by Gaia are improving the situation. Aims. Gaia's Early Data Release 3 (EDR3) offers higher astrometric precision and greater completeness compared to previous releases. Taking advantage of these improvements requires that the CSPNe in the catalogue be accurately identified. Methods. We applied our automated technique based on the likelihood ratio method to cross match know…
We have studied a sample containing about 6000 OB stars with proper motions and trigonometric parallaxes from the Gaia DR2 catalogue. The following parameters of the angular velocity of Galactic rotation have been found: $Ω_0=29.70\pm0.11$ km s$^{-1}$ kpc$^{-1}$, $Ω'_0=-4.035\pm0.031$ km s$^{-1}$ kpc$^{-2}$, and $Ω''_0= 0.620\pm0.014$ km s$^{-1}$ kpc$^{-3}$. The circular rotation velocity of the solar neighborhood around the Galactic center is $V_0=238\pm5$ km s$^{-1}$ for the adopted Galactocentric distance of the Sun $R_0=8.0\pm0.15$ kpc. The amplitudes of the tangential and radial velocity …
We analyze the spatial and kinematic properties of a large sample of young T Tauri type stars in a 500 pc radius solar neighborhood, closely related to the Gould belt. The following parameters of the exponential density distribution have been determined: the average $(z_G)_\odot=-25\pm5$ pc and scale height $h_G=56\pm6$ pc. We propose a method of excluding background stars from the samples, which are located at large heights with respect to the symmetry plane of the Gould belt. We discovered that the expansion effect for the entire star system, $K_G=6\pm1$ km s$^{-1}$ kpc$^{-1}$, is determined…
In this work, we use $13$ microlensing candidates with dark lenses from OGLE III catalogue \cite{2016MNRAS.458.3012W} and cross-match them with the GAIA catalogue. We identify the microlensing source stars in the GAIA catalogue by comparing the coordinate and the magnitude of stars and using the proper motion and the parallax parameters of the source stars. Combining with the microlensing light curves as well as the microlensing parallax effect, we determine the mass and the distance of lenses from Earth. We conclude that the lens for this set of microlensing events for the massive lenses are …
Context. Although the Gaia catalogue on its own is a very powerful tool, it is the combination of this high-accuracy archive with other archives that will truly open up amazing possibilities for astronomical research. The advanced interoperation of archives is based on cross-matching, leaving the user with the feeling of working with one single data archive. The data retrieval should work not only across data archives but also across wavelength domains. The first step for a seamless access to the data is the computation of the cross-match between Gaia and external surveys. Aims. We describe th…
Interpreting and modelling astronomical catalogues requires an understanding of the catalogues' completeness or selection function: objects of what properties had a chance to end up in the catalogue. Here we set out to empirically quantify the completeness of the overall Gaia DR3 catalogue. This task is not straightforward because Gaia is the all-sky optical survey with the highest angular resolution to date and no consistent ``ground truth'' exists to allow direct comparisons. However, well-characterised deeper imaging enables an empirical assessment of Gaia's $G$-band completeness across par…
Search for quasar pairs with Gaia astrometric data. II. Photometric redshift prediction with machine learning for the MGQPC catalogue
Institute for Frontier in Astronomy and Astrophysics, Beijing Normal University（北京师范大学前沿天文与天体物理研究院）；National Astronomical Observatories, Chinese Academy of Sciences（中国科学院国家天文台）；School of Physics and Astronomy, Beijing Normal University（北京师范大学物理与天文学院）
The second $Gaia$ Data Release (DR2) contains astrometric and photometric data for more than 1.6 billion objects with mean $Gaia$ $G$ magnitude $<$20.7, including many Young Stellar Objects (YSOs) in different evolutionary stages. In order to explore the YSO population of the Milky Way, we combined the $Gaia$ DR2 database with WISE and Planck measurements and made an all-sky probabilistic catalogue of YSOs using machine learning techniques, such as Support Vector Machines, Random Forests, or Neural Networks. Our input catalogue contains 103 million objects from the DR2xAllWISE cross-match tabl…
While Gaia has observed the phase space coordinates of over a billion stars in the Galaxy, in the overwhelming majority of cases it has only obtained five of the six coordinates, the missing dimension being the radial (line-of-sight) velocity. Using a realistic mock dataset, we show that Bayesian neural networks are highly capable of 'learning' these radial velocities as a function of the other five coordinates, and thus filling in the gaps. For a given star, the network outputs are not merely point predictions, but full posterior distributions encompassing the intrinsic scatter of the stellar…
Gaia GraL X.: The GraL catalogue of gravitationally lensed quasars Matched with \textit{Gaia} data, redshifts, and time delays
Laboratoire d’Astrophysique de Bordeaux, Univ. Bordeaux, CNRS（波尔多天体物理学实验室，波尔多大学，法国国家科学研究中心）；Instituto de Astronomia, Geofísica e Ciências Atmosféricas, Universidade de São Paulo（圣保罗大学天文、地球物理与大气科学研究所）；Donald Bren School of Information and Computer Sciences, University of California, Irvine（加州大学尔湾分校唐纳德·布伦信息与计算机科学学院）；CENTRA/SIM, Faculdade de Ciéncias, Universidade de Lisboa（里斯本大学理学院CENTRA/SIM）；Université Côte d’Azur, Observatoire de la Côte d’Azur, CNRS, Laboratoire Lagrange（蔚蓝海岸大学，蔚蓝海岸天文台，法国国家科学研究中心，拉格朗日实验室）；Sydney Institute for Astronomy, School of Physics, The University of Sydney（悉尼大学物理学院悉尼天文学研究所）；Center for Astrophysics Harvard & Smithsonian（哈佛-史密森尼天体物理中心）；Jet Propulsion Laboratory, California Institute of Technology（加州理工学院喷气推进实验室）
In this work we improve a previously published method to calculate in a reliable way the radius of an open cluster. The method is based on the behaviour of stars in the proper motion space as the sampling changes in the position space. Here we describe the new version of the method and show its performance and robustness. Additionally, we apply it to a large number of open clusters using data from Gaia DR2 to generate a catalogue of 401 clusters with reliable radius estimations. The range of obtained apparent radii goes from Rc=1.4+-0.1 arcmin (for the cluster FSR 1651) to Rc=25.5+-3.5 arcmin …
We present a sub-arcsecond cross-match of Gaia DR2 against the INT Photometric H-alpha Survey of the Northern Galactic Plane Data Release 2 (IPHAS DR2) and the Kepler-INT Survey (KIS). The resulting value-added catalogues (VACs) provide additional precise photometry to the Gaia photometry (r, i and H-alpha for IPHAS, with additional U and g for KIS). In building the catalogue, proper motions given in \gaia\ DR2 are wound back to match the epochs of IPHAS DR2, thus ensuring high proper motion objects are appropriately cross-matched. The catalogues contain 7,927,224 and 791,071 sources for IPHAS…
The body of photometric and astrometric data on stars in the Galaxy has been growing very fast in recent years (Hipparcos/Tycho, OGLE-3, 2-Mass, DENIS, UCAC2, SDSS, RAVE, Pan Starrs, Hermes, ...) and in two years ESA will launch the Gaia satellite, which will measure astrometric data of unprecedented precision for a billion stars. On account of our position within the Galaxy and the complex observational biases that are built into most catalogues, dynamical models of the Galaxy are a prerequisite full exploitation of these catalogues. On account of the enormous detail in which we can observe t…
Chronology of our Galaxy from Gaia Colour-Magnitude Diagram-fitting (ChronoGal). I. The formation and evolution of the thin disk from the Gaia Catalogue of Nearby Stars
We extend the SDSS Stripe 82 Standard Stars Catalog with post-2007 SDSS imaging data. This improved version lists averaged SDSS ugriz photometry for nearly a million stars brighter than r~22 mag. With 2-3x more measurements per star, random errors are 1.4-1.7x smaller than in the original catalog, and about 3x smaller than for individual SDSS runs. Random errors in the new catalog are ~< 0.01 mag for stars brighter than 20.0, 21.0, 21.0, 20.5, and 19.0 mag in u, g, r, i, and z-bands, respectively. We achieve this error threshold by using the Gaia Early Data Release 3 (EDR3) Gmag photometry to …
We present a method to identify Ultra Faint Dwarf Galaxy (UFDG) candidates in the halo of the Milky Way using the future Gaia catalogue and we explore its detection limits and completeness. The method is based on the Wavelet Transform and searches for over-densities in the combined space of sky coordinates and proper motions, using kinematics in the search for the first time. We test the method with a Gaia mock catalogue that has the Gaia Universe Model Snapshot (GUMS) as a background, and use a library of around 30 000 UFDGs simulated as Plummer spheres with a single stellar population. For t…
Based on astrometric data from Gaia DR2, we employ an unsupervised machine learning method to blindly search for open star clusters in the Milky Way within the Galactic latitude range of |b| < 20 degrees. In addition to 2,080 known clusters, 74 new open cluster candidates are found. In this work, we present the positions, apparent radii, parallaxes, proper motions and member stars of these candidates (https://cdsarc.u-strasbg.fr/ftp/vizier.submit//new_OC/). Meanwhile, to obtain the physical parameters of each candidate cluster, stellar isochrones are fit to the photometric data. The results sh…
The spatial and kinematic properties of a large sample of young T Tauri stars from the solar neighborhood 500 pc in radius have been studied. The following parameters of the position ellipsoid have been determined from the most probable members of the Gould Belt: its sizes are $350\times 270 \times 87$~pc and it is oriented at an angle of $14\pm1^\circ$ to the Galactic plane with a longitude of the ascending node of $297\pm1^\circ$. An analysis of the motions of stars from this sample has shown that the residual velocity ellipsoid with principal semiaxes $σ_{1,2,3}=(8.87,5.58,3.03)\pm(0.10,0.2…
We have selected a sample of 326 young $(\log t<8)$ open star clusters with the proper motions and distances calculated by various authors from Gaia DR2 data. The mean values of their line-of-sight velocities have also been taken from various publications. As a result of our kinematic analysis, we have found the following parameters of the angular velocity of Galactic rotation: $Ω_0=29.34\pm0.31$ km s$^{-1}$ kpc$^{-1}$, $Ω'_0=-4.012\pm0.074$ km s$^{-1}$ kpc$^{-2}$, and $Ω''_0=0.779\pm0.062$ km s$^{-1}$ kpc$^{-3}$. The circular rotation velocity of the solar neighborhood around the Galactic cen…
We present a catalogue of 551,214 main-sequence stars in the local ($d < 2$ kpc) Galactic thick disk and halo, based on a search of stars with large proper motions ($μ_{\mathrm{tot}} > 40.0$ mas/yr) in the Gaia Early Data Release 3. We derive photometric metallicity calibrated from the colour-luminosity-metallicity distribution of 20,047 stars with spectroscopic metallicities, collected from various spectroscopic surveys, including SDSS SEGUE/APOGEE, GALAH DR3, and LAMOST DR6. We combine these results to construct an empirical colour-magnitude-metallicity grid, which can be used to estimate ph…
We present a catalogue of point-like Hα-excess sources in the Northern Galactic Plane. Our catalogue is created using a new technique that leverages astrometric and photomeric information from Gaia to select Hα-bright outliers in the INT Photometric Hα Survey of the Northern Galactic Plane (IPHAS), across the colour-absolute magnitude diagram. To mitigate the selection biases due to stellar population mixing and to extinction, the investigated objects are first partitioned with respect to their positions in the Gaia colour-absolute magnitude space, and in the Galactic coordinates space, respec…
Aims. The Radial Velocity Spectrometer (RVS) on board the ESA satellite mission Gaia has no calibration device. Therefore, the radial velocity zero point needs to be calibrated with stars that are proved to be stable at a level of 300 m/s during the Gaia observations. Methods. We compiled a dataset of ~71000 radial velocity measurements from five high-resolution spectrographs. A catalogue of 4813 stars was built by combining these individual measurements. The zero point was established using asteroids. Results. The resulting catalogue has seven observations per star on average on a typical tim…
We have analyzed the kinematics of 9750 OB2 stars with proper motions and parallaxes selected by Xu et al. from the Gaia EDR3 catalogue. The relative parallax errors for these stars do not exceed 10\%. Based on the entire sample of stars, we have found the velocities $(U,V)_\odot=(7.17,7.37)\pm(0.16,0.24)$ km s$^{-1}$ and the components of the angular velocity of Galactic rotation: $Ω_0 =29.700\pm0.076$ km s$^{-1}$ kpc$^{-1}$, $Ω^{'}_0 =-4.008\pm0.022$ km s$^{-1}$ kpc$^{-2}$, and $Ω^{''}_0 = 0.671\pm0.011$ km s$^{-1}$ kpc$^{-3}$, where the linear rotation velocity of the Galaxy at the solar di…
Faint, hidden contaminants in the point-spread functions (PSFs) of stars cause shifts to their measured positions. Wilson & Naylor (2017) showed failing to account for these shifts can lead to a drastic decrease in the number of returned catalogue matches in crowded fields. Here we highlight the effect these perturbations have on cross-matching, for matches between Gaia DR2 and WISE stars in a crowded Galactic plane region. Applying the uncertainties as quoted to Gaussian-based astrometric uncertainty functions (AUFs) can lead, in dense Galactic fields, to only matching 55% of the counterparts…
We consider open star clusters (OSCs) with the proper motions, parallaxes, and line-of-sight velocities calculated by various authors from Gaia DR2 data. The distance scale factor has been found by analyzing the separate solutions of the basic kinematic equations to be $p=1.00\pm0.04.$ It shows that the distances calculated using the parallaxes from the Gaia DR2 catalogue do not need any correction factor. We have investigated the solutions obtained from various OSC samples differing in both age and accuracy of their parallax and line-of-sight velocity measurements. The solution obtained from …
The second Gaia data release (DR2), contains very precise astrometric and photometric properties for more than one billion sources, astrophysical parameters for dozens of millions, radial velocities for millions, variability information for half a million of stellar sources and orbits for thousands of solar system objects. Before the Catalogue publication, these data have undergone dedicated validation processes. The goal of this paper is to describe the validation results in terms of completeness, accuracy and precision of the various Gaia DR2 data. The validation processes include a systemat…
